User`s manual

6.4 Termination Resistors
No termination resistors are provided on the QSP-200/300 ports. Both output and
input signals are connected only to the external connector. Any termination which is
required must be added externally.
+
-
RS-422/485 Receiver
Rt
RXD+
RXD-
+
-
RS-422/485 Receiver
Rt
AUXIN+
AUXIN-
RS-422
100 ohm 1/2W resistor
RS-485
60 ohms total resistance
(120 ohms at each end)
Recommended Termination Resistor Values
Figure 7. RS-422/485 Termination
6.5 2-Wire Operation
The QSP-200/300’s ports may be configured for either full duplex or half duplex
operation. By default, the RS-422/485 ports are configured for full duplex operation
with the RS-422/485 output drivers always enabled.
In half duplex mode, the RS-422/485 transmitter may be enabled and disabled via the
RTS (request to send) or DTR (data terminal ready) signals. Both RTS and DTR are
controlled through the Modem Control Register of the 16550.
QSP-200/300 User's Manual 39